The present invention relates generally to gate valves and, more particularly, to gate valves adapted for stem back seating. Gate valves are commonly used to control fluid flow during drilling, completion and production phases of well operations. Typically, gate valves are operated by turning a hand wheel or other handle to actuate the gate to and from an open and closed position.
Gate valve back seating surfaces on the stem and the bonnet body serve to form a pressure seal between the stem packing chamber and the valve body chamber when replacement of the stem packing is needed. The back seating shoulder on the stem is back seated against a surface on the bonnet body. In normal gate opening and closing operations, the stem is axially fixed and raises and lowers the gate by rotation since the stem and lift nut are matingly threaded. Therefore, in order to effect back seating, the bonnet cap must usually be unscrewed to allow the stem to be moved axially upward until the backseat shoulder on the stem contacts the bonnet body. A large amount of torque is often required to loosen the bonnet cap. In many instances torque-assisting tools such as chain tongs are needed to loosen the bonnet cap. Employing such torque-assisting devices presents potential hazards and adds to costs and operational time.
It is, therefore, an object of the present invention to provide effective and practical means for low torque back seating of gate valves. The present invention achieves this objective by implementing a stem and bonnet assembly having a rotatable bearing ring to which the stem is fixed during normal gate opening and closing operations, and the bearing is then fixed to the bonnet cap and the stem is released therefrom during back seating.